Unless otherwise indicated herein, the materials described in this section are not prior art to the claims of this application and are not admitted to be prior art by inclusion in this section.
Phase-change memory or phase-change random access memory (PCM or PRAM) is a non-volatile random access memory that has moved from research prototypes to commercial products. A PRAM cell may be constructed from germanium-antimony-tellurium (GST) material that may have a high melting point (approximately 620 Celsius). A PRAM cell may have various crystallization states (phases). In one phase, the GST material may be amorphous, resulting in a relatively high resistance value. In another phase, the GST material may be substantially crystalline, resulting in a relatively low resistance value.
For example, in a multilevel cell (MLC) PRAM having two resistance levels (e.g., a “2-level PRAM”), the low resistance value may be associated with logical “0,” whereas a high resistance value may be associated with a logical “1.” If a logical “1” is to be written to the 2-level PRAM, the PRAM cell may be configured to the amorphous state. If a logical “0” is to be written to the 2-level PRAM, the PRAM cell may be configured to the crystalline state, which has a relatively lower resistance level as compared to the amorphous state. When reading information from the PRAM cell, the resistance level may be measured to determine the information written to the PRAM cell.
PRAMs can be vulnerable to resistance drifts which may cause errors when performing a read operation on a PRAM. A resistance drift may be in the form of a change in resistance level over time caused by changes in the GST material. The resistance drift can cause an erroneous condition in which the information stored in the MLC PRAM may be different than what is read due to the change in resistance level. In some applications, the resistance drift can be a significant issue. In some instances, a 4-level MLC PRAM with soft error rate of 6.74×10−5 can incur 9.26×106 errors, for example, which is nearly one million times larger than that of dynamic RAM (DRAM).